You are going to find many different stories indicating that a brand/model is better than the other. I've read 100s of reviews (part of my job) on these base gateway/router models and find that the D-Links do get better reviews on the net. However, I know that I've read a bunch of stories on this, and other sites, that the D-Link604 model as well as the equivilant wireless model, fry very easily. I've read very few similar stories about Linksys.
Support is also a concern. I read this story on PCWorld.com about a guy calling D-Link support and the tech ended walking him through utter descruction of his PC's settings just to get the product to work correctly. Haven't read too many similar stories about Linksys support.
Linksys products are now manuf. by Cisco. Linksys still has their own support team, but the product itself is trusted with a Cisco brand name (not too shabby!).
I've read more stories about users liking the user interface from the D-Link better than the Linksys products. And, I know for a fact that D-Link really strives to get the product working in as least time as possible right out of the box. Linksys does a pretty good job at this too....but not to match with D-Link.
All, in all I feel that I've had better luck with Linksys and I'll always begin to trust their name over any other home gateway/router product on the market.
SMC makes an excellent line of products as well. But, out of the box, they are NOT user friendly.
-Mike